Multi-wavelength Polarization Mirau Interference Microscope for Micro Profile Transient Measurement
Micro-optical components have been widely adopted in intelligent device imaging,medical devices,and national defense security due to their high degree of freedom and arrayability.The inspection is particularly important to ensure processing accuracy prior to use.Interferometric microscopy is the authoritative high-precision micro-profile inspection technology.However,the measurement range of single wavelength interferometry is limited by the wavelength,making it insufficient to detect optical devices with high degrees of freedom.Moreover,the traditional PZT phase shift is vulnerable to environmental disturbances and can cause drive hysteresis when measuring at multiple wavelengths.The multi-wavelength polarization Mirau interference microscope for transient micro profile detection is proposed to address the issues of narrow measurement range and 2π ambiguity in single wavelength Mirau interference microscopes,enabling the testing of surface figure with large dynamic range and surface roughness of microscopic structures.It provides a simple and elegant solution to these problems that arise in the aforementioned interferometric microscopy measurements.This measurement system utilizes a splitter prism to gather three monochromatic LEDs as a multi-wavelength light source.In order to meet the testing requirements for various tested objects with different reflectivity,a linear grid polarizer is employed as a polarized beam splitter in the proposed system,to achieve polarization splitting and adjustable fringe contrast.The color polarization camera only needs to capture one image to decompose and obtain color phase-shifting interference fringes with a phase shift of π/2 in the three RGB channels.By using a four step phase shifting algorithm to calculate the transient wavefront distribution corresponding to the three wavelengths R,G,and B.Based on multi-wavelength interference technology,the accurate optical path difference between the reference light and the detection light at each pixel point can be obtained,thereby achieving instantaneous detection of the surface profile to be measured.Multi-wavelength phase shift interferometry can use measurement results of different wavelengths to correct the stripe order.By comparing the measurement results of three different wavelengths in pairs,it can simultaneously compensate for the shortcomings of single wavelength and dual-wavelength measurements.Using single wavelength interference and multi-wavelength interference to measure diamond turning convex mirrors,stripe order correction can be achieved through interference measurement results of different wavelengths,and the deviation in PV values between single wavelength and multi wavelength measurement results is less than 10 nm.The color polarization camera is the foundation for realizing transient detection in this system.In practical measurement,different incident wavefronts cause changes in the field of view error in the polarization camera and increase with the increase of wavefront slope,resulting in certain measurement errors.The cubic spline interpolation method using adjacent reconstructed pixels is adopted to correct the field of view error of the polarization camera.After correction,the PV value of phase error for the polarization camera is significantly reduced.Multi-wavelength polarization Mirau interference microscope was set up,and the micron step with the nominal value of 1.993 9 μm was measured after correcting system error with calibration data,and the deviation from the nominal value was about 5.4 nm.Comparing the single wavelength and multi-wavelength measurement results of the diamond turning convex mirrors surface profile with the measurement results of the Wyko,the detection results corrected by multi-wavelength interference technology are close to the surface profile distribution of the Wyko,indicating the feasibility of this transient measurement system for micro profile.Comparing the measurement results of the surface roughness of diamond turning convex mirrors,the results show that the RMS value deviation of the micro profile transient measurement method based on multi-wavelength interference technology compared to the measurement results of Wyko interferometer is 3.7 nm.The profile curves measured by the two measurement systems are very consistent,verifying that the system can achieve high-precision and large dynamic range measurement.
万方数据
维普
